Heater while on hot starts blowing cold
 

I have a 2005 Hummer H2 that will stop blowing hot air and start blowing cold without touching it. It is like someone turned on the AC. I have notice that it does it when on defrost. I normally have it around 85 degree as it has to be turn up a lot to heat up the space. Then all by itself it wil blow cold on both sides. Without touching it it will go back to hot after a few minutes. I have check to see if it has thrown any codes but it has not. Any ideas what to look for? Thanks :confused:

Mine is doing the same thing. I think it has something to do with the vent flaps that control where the air is coming out (defrost, the front vents, the floor...) I'm not sure if its a vacuum leak or if they are electric motors. Once i get my t-case fixed this will be the next thing i have to address

Keep me posted if you get your find out what is causing it and I will do the same. Right now I have it parked in the garage until this weekend as both of my front wheel bearings need to be replaced.

Mine does the same thing. ('07 H2) Mine also only blows hot air when set to 90. Anything below and it's cold. Heading to the dealership Monday, I'll post with what they find.

Hey Markcore what did you find out?

Just got a call from the dealership...

They said that at 90 it will over ride the computer and blow out hot air. Anything less, there is a sensor the monitors the cabin air temp to make the inside air temp to what you set it too. IE: when you put your setting to 89 it will make the cabin temp to 89 degrees. Well, the reason why my truck would blow out cold air at 89 and hot at 90 was, when at 90 it would over ride it and at 89 the computer was getting a reading of 220 degrees. HA! So I had a bad inside air temp sensor.

Hope this helps you guys!